// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Provides a way to handle exceptions that happen while a WindowProc is
// running. The behavior of exceptions generated inside a WindowProc is OS
// dependent, but it is possible that the OS just ignores the exception and
// continues execution, which leads to unpredictable behavior for Chrome.

#ifndef BASE_WIN_WRAPPED_WINDOW_PROC_H_
#define BASE_WIN_WRAPPED_WINDOW_PROC_H_

#include <windows.h>

#include "base/base_export.h"
#include "base/strings/string16.h"

namespace base {
namespace win {

    // An exception filter for a WindowProc. The return value determines how the
    // exception should be handled, following standard SEH rules. However, the
    // expected behavior for this function is to not return, instead of returning
    // EXCEPTION_EXECUTE_HANDLER or similar, given that in general we are not
    // prepared to handle exceptions.
    typedef int(__cdecl* WinProcExceptionFilter)(EXCEPTION_POINTERS* info);

    // Sets the filter to deal with exceptions inside a WindowProc. Returns the old
    // exception filter, if any.
    // This function should be called before any window is created.
    BASE_EXPORT WinProcExceptionFilter SetWinProcExceptionFilter(
        WinProcExceptionFilter filter);

    // Calls the registered exception filter.
    BASE_EXPORT int CallExceptionFilter(EXCEPTION_POINTERS* info);

    // Initializes the WNDCLASSEX structure |*class_out| to be passed to
    // RegisterClassEx() making sure that it is associated with the module
    // containing the window procedure.
    BASE_EXPORT void InitializeWindowClass(
        const char16* class_name,
        WNDPROC window_proc,
        UINT style,
        int class_extra,
        int window_extra,
        HCURSOR cursor,
        HBRUSH background,
        const char16* menu_name,
        HICON large_icon,
        HICON small_icon,
        WNDCLASSEX* class_out);

    // Wrapper that supplies a standard exception frame for the provided WindowProc.
    // The normal usage is something like this:
    //
    // LRESULT CALLBACK MyWinProc(HWND hwnd, UINT message,
    //                            WPARAM wparam, LPARAM lparam) {
    //   // Do Something.
    // }
    //
    // ...
    //
    //   WNDCLASSEX wc = {0};
    //   wc.lpfnWndProc = WrappedWindowProc<MyWinProc>;
    //   wc.lpszClassName = class_name;
    //   ...
    //   RegisterClassEx(&wc);
    //
    //   CreateWindowW(class_name, window_name, ...
    //
    template <WNDPROC proc>
    LRESULT CALLBACK WrappedWindowProc(HWND hwnd, UINT message,
        WPARAM wparam, LPARAM lparam)
    {
        LRESULT rv = 0;
        __try {
            rv = proc(hwnd, message, wparam, lparam);
        } __except (CallExceptionFilter(GetExceptionInformation())) {
        }
        return rv;
    }

} // namespace win
} // namespace base

#endif // BASE_WIN_WRAPPED_WINDOW_PROC_H_
